Let say the equation of travelling wave is
[tex]y_i = A sin(wt - kx)[/tex]
now if the wave is reflected such that it is not inverted after reflection
So the equation of reflected wave will be
[tex]y_r = A sin(wt + kx)[/tex]
now we will have
[tex]y = y_i + y_r[/tex]
now we will have
[tex]y = Asin(wt - kx) + Asin(wt + kx)[/tex]
[tex]y = A[2sin(\frac{(wt - kx) +(wt + kx)}{2})cos(\frac{(wt - kx) -(wt + kx)}{2})][/tex]
[tex]y = 2Acos(kx)sin(wt)[/tex]
so above equation shows the condition of standing waves